idx: Switch WalkIndexFile to accept generic io.ReaderAt

This is necessary to use it with in-memory idx files.

weed/storage/idx/walk.go

@@ -11,11 +11,17 @@ import (
 
 // walks through the index file, calls fn function with each key, offset, size
 // stops with the error returned by the fn function
-func WalkIndexFile(r *os.File, fn func(key types.NeedleId, offset types.Offset, size uint32) error) error {
+func WalkIndexFile(r io.ReaderAt, fn func(key types.NeedleId, offset types.Offset, size uint32) error) error {
 	var readerOffset int64
 	bytes := make([]byte, types.NeedleMapEntrySize*RowsToRead)
 	count, e := r.ReadAt(bytes, readerOffset)
-	glog.V(3).Infoln("file", r.Name(), "readerOffset", readerOffset, "count", count, "e", e)
+	var name string
+	if f, ok := r.(*os.File); ok {
+		name = f.Name()
+	} else {
+		name = "memory"
+	}
+	glog.V(3).Infoln("file", name, "readerOffset", readerOffset, "count", count, "e", e)
 	readerOffset += int64(count)
 	var (
 		key    types.NeedleId
@@ -35,7 +41,7 @@ func WalkIndexFile(r *os.File, fn func(key types.NeedleId, offset types.Offset,
 			return nil
 		}
 		count, e = r.ReadAt(bytes, readerOffset)
-		glog.V(3).Infoln("file", r.Name(), "readerOffset", readerOffset, "count", count, "e", e)
+		glog.V(3).Infoln("file", name, "readerOffset", readerOffset, "count", count, "e", e)
 		readerOffset += int64(count)
 	}
 	return e